The invention relates to a semipermeable membrane consisting of a polymer containing aryl groups which embodies [--SO.sub.3 --] groups.
Semipermeable membranes of this type are known. Thus, ICJL-RD 210-009 (Imperial Chemical Industries Limited Research Disclosure) describes semipermeable membranes which are formed by sulphonated polyaryl ether sulphone polymers in which (--SO.sub.2 --) groups occur in the chains as well as [--SO.sub.3 --] groups coupled to the chains. Membranes of this type are suitable, inter alia, for hyperfiltration, reasonably good retentions and fluxes being obtained for salt; salt retentions greater than 90% and fluxes greater than 40 liter/m.sup.2.h.bar at 40 bar are generally not achieved.
An important disadvantage of such sulphonated polyaryl ether sulphone polymers is their relatively low thermal stability. As a result, use of membranes of this type above 80.degree. C. is not possible; above said temperature deformation and impairment of properties occurs.